Abstract
The first half of biosynthetic pathway of chlorophyll (Chl) is shared with heme biosynthesis. Mechanisms by which the two major tetrapyrroles, Chl and heme, are allocated appropriately in photosynthetic cells are remained unknown. Mg-chelatase, consisting of the three subunits ChlI, ChlD and ChlH, is the first enzyme in Mg-branch, and this enzyme is supposed to play an important role in the teterapyrrole allocation mechanism. In this study, we cloned the chlD gene encoding one subunit of Mg-chelatase from the cyanobacterium Plectonema boryanum, which is capable of growing heterotrophically in the dark, and tried to isolate a chlD-disrupted mutant by screening in the dark. Southern blot analysis indicated that a resulting mutant A5101 is a single recombinant. However, A5101 did not grow photoautotrophically and the Chl content was only about 10% of wild type. Further phenotypic analysis will be presented and the function of ChlD is also discussed.
